Heat developable diazotype material comprising an unsymmetrical urea as the base release agent



nite States HEAT DEVELOPABLll DIAZOTYPE MATERIAL COMPRISING AN UNSYMMETRIEAL UREA AS THE BASE RELEASE AGENT Elliot Berman, Braintree, Hollis E. French, Woburn,

David S. Most, Peabody, Richard D. Murray, Restindaie, and Richard R. Roberts, Concord, Mass., assignors to ltek Corporation, Lexington, Mass., a corporation of Delaware No Drawing. Filed Aug. 28, 1962, Ser. No. 220,681 5 Claims. (Cl. 96-9ll) This invention relates to diazotype reproduction sys tems. More particularly, this invention relates to completely dry diazo copying systems.

The term ream as used herein is 500 sheets.

Diazotype reproductions are now made by two processes, that are generally referred to as the dry process and the semidry process. Both processes are based upon the ability of diazo compounds to form azo dyes with coupling components.

In the dry process, the sensitized paper is coated with a sensitizing layer that contains both a diazo compound and a coupler, together with acids and stabilizing materials that are intended to prevent thermal decomposition of the diazo compound and premature coupling. After exposure of the paper to actinic light, development is caused to occur by bringing the exposed paper into contact with ammonia fumes, at an elevated temperature. The ammonia fumes change the pH of the sensitized coating so as to permit coupling to occur. The equipment that is required for this process usually requires permanent installation, with adequate venting to remove the fumes. Consequently, the dry process is used primarily in centralized reproduction systems, where adequate precautions can be taken to keep the fumes from personnel.

In the semidry process, the hazard of ammonia fumes is eliminated through the use of a developing solution that is applied directly to the exposed paper, and that usually contains a coupler in addition to an agent to produce the proper pH to permit coupling to occur. The sensitized paper, that is used in the semidry process, is coated with a sensitizer layer that contains a diazo compound and one or more stabilizers. The developing solution brings the coupler into contact with the diazo compound, and also maintains an alkaline environment that permits coupling to occur. This process requires careful handling of the developing solutions, that are usually corrosive and highly alkaline. Moreover, the choice of diazo and coupler materials is limited because the wet conditions of development favor bleeding.

For many years, there has been a substantial interest in heat developable diazo systems, since this type of system would be completely dry and free from fumes. While there has been speculation about and work on such systems for many years, each proposal in the past has suffered from some disadvantage that to date has prevented its commercial adoption.

One of the early attempts to solve the problem involved the use of a dusting technique. Paper coated with a diazo compound was dried and then dusted over with a finely powdered mixture of a coupler and an alkaline-reactive substance. This early approach suffered from the disadvantage that the handling and distribution of the powder were difiicult, and the reproductions were not uniform. Other systems have been suggested that are similar to the powder technique in that they involve the physical separation of the diazo and the coupler. Some of these physical separation techniques have involved a great deal of ingenuity, but usually there has been some major drawback, such as discoloration of the senstized paper caused by precoupling, or very slow development caused by the restraint applied by the physical separation means on the coupling process.

Another approach to the problem, in addition to the physical separation approach, has utilized a chemical system that is non-reactive at ordinary temperatures but that is activated by heat. In one example of this approach, aryl diazo sulfonates were employed as sensitizing agents. These substances do not couple with azo components unless activated by heat. In another example of this approach, the sensitized layer was made acidic to inhibit coupling, with the diazo material and coupler present in the sensitized layer, and a base release material was applied to the paper as a separate coating, to decompose upon being heated, to change the pH to permit coupling to occur.

Unfortunately, it has proved extremely difiicult to use any of these expedients to produce a dry diazotype reproduction material, and at the same time to achieve the balance of print density, exposure speed, shelf stability, and developing speed and temperature, that is necessary in order to gain commercial acceptance.

One object of the present invention is to provide a practical, commercially acceptable, completely dry diazo copying system.

Another obejct of the invention is to provide a practical, dry reproduction process that produces a fixed print, i.e., a print that is of permanent quality.

Another object of the invention is to provide a positive working, heat developable, light-sensitive diazotype formulation that permits a practical dry reproduction process,

A further object of the invention is to provide a practical, heat developable diazotype material that involves only a single coating step for the application of the material to a support, such as paper.

Another object of the invention is to provide a diazotype formulation that permits dry reproduction and that provides a practical and commercial acceptable balance of characteristics as to print density, print speed, shelf life, and developing speed and temperature.

A further object of the invention is to provide a heat developable diazotype formulation that is characterized by a minimal tendency to precouple even under the extreme conditions of high temperatures and high relative humidities that may occur during hot summer months.

A more specific object of the invention is to provide a practical, positive working, heat developable, light sensitive diazotype material in which development is caused to occur by the thermal decomposition of a base release material.

A related object of the invention is to provide a practical, positive working, heat developable, light sensitive diazotype material in which development is caused to occur by the thermal decomposition of a base release material, and wherein the light sensitive and base release materials are incorporated in a single coating on a base, and that is characterized by commercially acceptable product stability together with ease of heat development of the image.

A further object of the invention is to provide practical processes for making products of the character described.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

We have found that a practical, positive working, heat developable, light sensitive diazotype material, that has a satisfactory balance of characteristics as to-print density, print speed, shelf stability, and developing speed and temperature, may be obtained by applying to a paper base a sensitizing coating comprising a balanced formulation of a diazo compound, coupling material, stabilizer, and a particular kind of base release material. The base release materials that are used, in accordance with this invention,

sac-ace? are the unsymmetrical disubstituted ureas, particularly, N,N-dialkylureas, and preferably, those in which the alkyl substituents are lower alkyl substituents such as, for example, N,N-diethylurea. The terrrr lower alkyl is used to refer to alkyl groups containing not more than four carbon atoms, i.e., methyl, ethyl, propyl and butyl groups. These materials may be used alone or in combination with other base release materials, such as, for example, urea. The coating may also contain auxiliary substances that are often incorporated in diazotype light sensitive formulations.

In accordance with a preferred embodiment of the invention, the base paper or other support, on which the light sensitive layer is coated, is formed with a precoat of a film-forming material that preferably contains a material such as colloidal silica or the like. The precoat is useful for assisting in controlling the speed of printing and the speed of developing.

Sensitized paper, that is made in accordance with this invention, is exposed under ultraviolet light in a conventional manner, to form latent images. The latent image is developed by passing the paper through a heating zone that decomposes the base release material, to change the pH of the sensitized coating so as to permit coupling and development to occur. The heat may be applied in any convenient manner, as by passing the exposed paper into contact with a heated roller, or subjecting it to infrared radiation from a lamp, or by passing it through a ther mographic machine. Any convenient method of transferring the necessary heat to the exposed sensitive coating is satisfactory. However, while the use of such heat transfer methods as subjecting the exposed paper to steam, or to hot ammonia fumes, are operative, such techniques fail to exploit the full advantages of the present invention, which permits development under dry condi tions, free from objectionable fumes.

In making the positive working, heat developable, light sensitive diazotype material in accordance with this invention, the support for the light sensitive layer preferably is one of the several papers that are offered commercially for diazo coating. The precoat is applied to the selected paper in any convenient manner, such as, for example, by roll coating. The sensitizing coating is applied over the precoat either by roller coating, or by the use of an air knife, or by other convenient and practical methods.

One purpose of the precoat is to provide a film at the surface of the paper, to maintain the sensitized layer, that is to be applied over the precoat, at the surface. In this way, any interference with the reproduction, that might originate with the fibers or other elements of the paper, is minimized or is completely eliminated. Numerous polymeric film-forming materials are available for use in the precoat. One preferred precoating material is polyvinyl acetate, which can be conveniently applied to the surface of the paper in an aqueous solution. Other filmforming materials may also be used including, by way of further example, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxye-thyl cellulose, gelatin, and sodium carboxymethyl cellulose.

The precoating solution preferably also contains a material such as colloidal silica, that has been found useful in diazo coating operations, for increasing the density of the prints that are obtained. Other materials that may be employed, instead of the colloidal silica, include dispersions of aluminum oxide, titanium dioxide, barium sulfate, and the like. An acid or acidic material may also be incorporated in the precoating solution to control its pH. Suitable pH control agents are citric, tartaric, and boric acids.

The sensitizing solution contains a diazo compound, coupling material, one or more stabilizers, base release material, and auxiliary substances such as are commonly employed in diazotype formulations. Optimum results are obtained when the diazo material is a stable, relatively slow diazo. Preferred materials include p-diazoi N-diethyl-m-phenetidine-%-zinc chloride and p-diazodiphenylamine sulfate, or other stable salts of these diazo compounds. Other diazo compounds can also be used, with the exercise of proper care in formulation to obtain a good balance of the desired characteristics, when acting in combination with the other necessary components of the formulation. The diazo compounds are preferably used, as is customary, in the form of salts, stabilized with zinc chloride, tin chloride, cadmium chloride and the like.

The coupling material must be carefully selected to obtain the desired result. To obtain the desired color together with satisfactory reactivity, it is usually necessary to use a combination of coupling components to obtain a balance of color and reactivity. A moderate coupling activity is preferred. Optimum results are usually obtained, therefore, when the coupling material comprises two or more coupling components that are present in the proper proportions to provide the desired balance between color and reactivity. For example, good results have been obtained by using, as the coupling material in the sensitizing solution, a blend of phloroglucinol and the sodium salt of 2,3-dihydroxynaphthaline-6-sulfonic acid. Other coupling components may also be used, such as, for example, 3-hydroxy-2-naphthoic acid, fl-naphthol, pyrogallic acid, resorcinol, Z-hydroxy naphthoic acid monoethanol amide, and the like.

The base release material may be, for example, a 1,1- dialkyl derivative of urea, or a mixture of the disubstituted urea with urea or other base release material. The unsymmetrical disubstitutcd urea derivative preferably is a lower alkyl derivative, and optimum results are obtained when it is N,N-diethylurea.

The unsymmetrical disubstituted urea derivatives decompose thermally at elevated temperatures and are effective in heat developable diazotype formulations for permitting development to occur. They are particularly advantageous because they are very stable at room temperatures and therefore do not promote precoupling. While they may be used in the absence of any other thermal base release material, they may also be employed in comnation with one or more other thermal base release materials such as, for example, urea, monomethylurea, and monoethylurea. When such combinations are used, the relative proportions of the respective base release agents should be adjusted in accordance with the characteristics of the other components of the diazotype formulation. In any case, the amount of the base release material, other than the unsymmetrical disubstituted urea, should be held at a level that is sufficiently low so that precoupling at room temperature is avoided; the precise amount in a particular formulation will depend upon the reactivities of the diazo compound, coupler, and stabilizer, as well as on the decomposition (or dissociation) rate of the second base release material at storage temperatures.

A stabilizer, to control the pH of the sensitizing solution to restrain coupling, should also be included, such as, for example, citric acid or one of the other many acids that are commonly employed in diazotype material for this purpose. Such other suitable acids include, by way of example, acetic acid, tartaric acid, boric acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 3-nitrophthalic acid, and the lke.

Other auxiliary substances that may be incorporated in the sensitizing solution include, for example, stabilizing agents or materials for inhibiting discoloration of the prints after they are made, such as thiourea, thiosinamine, naphthalene trisulfonic acid and the like; a substance that is intended to reduce the tendency of the paper to curl, such as ethylene glycol, glycerol, or a polyethylene glycol; metal salts, such as are used for intensification of the dyestulf image, such as, for example, zinc chloride, ammonium sulfate, nickel sulfate, and the like; coating aids such as colloidal silica and the like; a small amount of a wetting agent such as saponin, lauryl sulfonate, cetyl ben- TABLE 1 Active Component Exemplary Material Parts Diazo compound p-diazo-N-diethyl-m- 0.3-7.0

phenetidine-%-Znlr. Coupler:

Fast coupler Phloroglucinol 0.3-7.0 Slow coupler 2,3-dihydroxynapthalcne-6- 0.3-100 SOaNa. Stabilizing agent Citric acid l 1.0 Unsymmetrical Dialky1urea N,N-diethylurea Other base release agent Urea 1 Or as needed to hold the pH below about 3.0.

The specific compounds, that are listed in Table 1 as exemplary materials, are identified for the purpose of illustrating the invention, and it is to be understood that other equivalent chemicals may be substituted for those identified, where functionally equivalent.

In preparing a diazo sensitizing solution in accordance with this invention, the components are selected to perform the functions described in Table 1 and are mixed, in appropriate proportions, together with appropriate amounts of auxiliary substances as previously described. These are all dissolved in water. The final pH of the solution is adjusted to be about 2.4, usually by small additions of citric acid or other appropriate material.

When a precoat is employed, it is applied at a rate sufiicient to deposit solids on a paper base at a rate on the order of from about 1.5 to about 5 lbs. per ream of 24" by 36" paper. The solids in the precoat comprise primarily the film-forming material, together with a minor amount of a material such as colloidal silica. The sensitizing solution is applied to the precoated paper at a rate that is sufiicient to increase the Weight of the precoated paper, per 24 by 36" ream, by from about 1.5 to about 4.0 lbs. The foregoing and following references to coat weights are on a dry basis.

The invention will be more fully understood from the following specific example, that should be understood to be illustrative only.

Example 1 A sensitizing solution was prepared from the following materials.

Material: Parts p-Diazo-N-diethyl-m-phenetidine-% -ZnCl 0.9 Phloroglucinol 0.5 2,3-dihydroxynaphthalene-6-So Na 1.3 Citric acid 1.0 Urea 5.0 N,N-diethylurea 5.3 Ethylene glycol 2.7 Thiourea 10.0 Zinc chloride 4.0 Saponine 0.1 Colloidal silica, solids 5.0 Water 64.2

This solution was roller coated on a white base paper having a weight of 14 lbs. per 17" by 22" ream, or 32 lbs. per 24" by 36" ream, to deposit 2.25 lbs. of the sensitizing material, dry basis on the base paper per 24" by 36" ream.

Paper sensitized in this manner was exposed in the ordinary way, under a transparent original drawn in penoil, in an exposure apparatus equipped with a high-pressure mercury vapor lamp.

The exposed paper was then developed by subjecting it to a temperature of 350 F. for 12 seconds. The prints that were obtained in this manner had very good density and were clean and sharp. The stability of the paper was satisfactory both before and after printing.

Example 2 A sensitizing solution was prepared from the following materials.

Material: Parts p-Diazo-N-diethyl-m-phenetidine-% -ZnCl 1.52 Phloroglucinol .64 2,3-dihydroxynaphthaline-6-So Na 1.73 Citric acid 1.82 N,N-diethylurea 6.06 Ethylene glycol 3.09 Thiourea 1 1.4 Zinc chloride 4.55 Saponine .11 Colloidal silica, 30% solids 2.84 Polyvinyl acetate solution, medium viscosity 15.1 Water 5 1.5

This solution coated on white base paper as in Example 1 produced satisfactory prints following exposure and heat development, and was stable both before and after printing.

Example 3 Example 4 A precoating composition was prepared from the ingredients tabulated below.

Material: Parts Polyvinyl acetate solution, medium viscosity 21.0

Colloidal silica, 18% solids 39.0

Citric acid 0.65

Water 39.4

The amount of citric acid employed was sufficient to adjust the pH to Within the range from about 3.9 to 4.1. This precoating composition was applied to a base paper,

'of the same kind that was used for Example 1, by roller coating onto the paper a suflicient quantity of the composition to increase the weight of the paper, per 24" by 36" ream, by 1.84 lbs.

The precoated paper was then roller coated with the sensitizing solution of Example 1, to deposit 2.54 lbs. of sensitizing material on the paper per 24" by 36" ream. A substantial improvement in image density was observed, as compared to the paper produced in Example 1, even at faster exposure speeds. The shelf life of both the unexposed paper and of the prints was improved as compared to the paper produced in Example 1.

To demonstrate a diiferent Way of making the sensitized paper, the procedure just described for making the paper Was modified by apply the precoat and the sensi- Comparable, satisfactory Example A sensitizing solution was prepared from the materials that are tabulated below, where the figures in the first column of figures represent a preferred formulation, and where the figures in the second column of figures represent preferred ranges from which selections can be made.

Material I Parts 1 Ranges 2-ethoxy-4-N,N-diethylarninodiazoben- 3. 5 2.010.0.

zone zinc chloride double salt. Phloroglucinol 1. 8 1.0-5.0. 2-hydr0xy naphthoie acid monoethanol 1. 8 1.0-5.0.

amide. 'Iartaric acid 3. 5 1.0-5.0. N,N-diethylurea 5.4 1.0- ".0. EthanoL. 14 Up to 50% of total solvent.

Water 70 As needed.

This formulation was applied to precoated paper as in Example 3. Good prints were obtained by ordinary exposure and heat development.

Urea, monomethyl urea, monoethyl urea, and other thermal base release materials can be added to this formulation, and can also be substituted for up to about 50% of the N,N-diethylurea in most cases, without material adverse effect. The use of an alcohol solvent facilitates coating.

Other demonstrations of the invention, employing other diazo compounds, couplers, thermal base release agents, acids, and auxiliary substances, than those named in the specific examples above, but following the teachings of the specification in general, have been made and favorably evaluated. While the diazotype compositions of this invention are intended to permit dry heat development, with complete freedom from fumes, should it be desired to do so for any reason, the exposed papers can be developed by ammonia fumes or by solutions of ammonia, or amines, or other materials ordinarily used for the purpose.

Diazotype papers that are made in accordance with this invention offer a balance of characteristics with regard to print density, print speed, shelf life, and developing speed and temperature, that are practical and that meet the demands of present day commercial practice. The papers are simple to manufacture since all of the active components can be applied in a single sensitizing coating composition at a single time. Moreover, prints made from these papers, as well as the papers themselves, have good stability during storage.

Prints that are made in accordance with this invention are completely dry prints and have the advantage of being fixed, that is. permanent, in the sense that a renewed application of either actinic light or heat will not obliterate or destroy the print. This is a decided advantage as compared to prints that can now be obtained from other dry reproduction processes.

As used in the claims hereafter, the term diazo compound is used as inclusive of diazonium salts; and the reference to proportional parts by Weight is intended to convey the sense that the parts recited are described in their relationship to each other rather than in obsolute terms.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the inventions, following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

What is claimed is: 1. A positive working, heat developable, light sensitive diazotype composition, comprising:

a support; and a light sensitive layer thereon comprising a light sensitive diazo compound, an azo coupling compound, an acidic stabilizing agent, and a thermally activatahle base release material in intimate admixture with said diazo compound, said coupling component and said stabilizing agent, said base release material having the general formula where x is a number between 1 and 4.

2. The diazotype material of claim 1 wherein said base release material is N,N-diethylurea.

3. The diazotype material of claim 1 wherein said light sensitive diazo compound is chosen from the group consisting of p-diazo-diethyl-m-phenetidine-%-zinc chloride and p-diazodiphenlyamine sulfate.

4. The diazotype material of claim 1 wherein said 2120 coupling component is chosen from the group consisting of phloroglucinol with the sodium salt of 2,3-dihydroxynaphthaline--sulfonic acid,

3-hydroxy-2-naphthoic acid,

pyrogallic acid,

resorcinol, and

2-hydroxy naphthoic acid monoethanol amide.

5. The diazotype material of claim 1, wherein said acidic stabilizing agent is chosen from the group consisting of citric acid,

acetic acid,

tartaric acid,

boric acid,

succinic acid,

glutaric acid,

adipic acid,

pimelic acid,

suberic acid,

azelaic acid,

sebacic acid and 3-nitrophthalic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,732,299 Morrison Jan. 24, 1956 3,027,256 Klimkowski et al. Mar. 27, 1962 3,046,128 Klimkowski et al. July 26, 1962 FOREIGN PATENTS 1,249,913 France Nov. 28, 1960 OTHER REFERENCES Handbook of Chemistry & Physics, 38th edition, 1956 1957, Chemical Rubber Publishing Co., Cleveland, Ohio, pages 1204-1205. 

1. A POSITIVE WORKING, HEAT DEVELOPABLE, LIGHT SENSITIVE DIAZOTYPE COMPOSITION, COMPRISING: A SUPPORT; AND A LIGHT SENSITIVE LAYER THEREON COMPRISING A LIGHT SENSITIVE DIAZO COMPOUND, AN AZO COUPLING COMPOUND AN ACIDIC STABILIZING AGENT, AND A THERMALLY ACTIVATABLE BASE RELEASE MATERIAL IN INTIMATE ADMIXTURE WITH SAID DIAZO COMPOUND, SAID COUPLING COMPONENT AND SAID STABILIZING AGENT, SAID BASE RELEASE MATERIAL HAVING THE GENERAL FORMUAL 